The present invention relates to a position informing apparatus, and more particularly, to a position informing apparatus used in a position information service in which the position of a portable cellular phone is informed in the event of an emergency report, or in which the geographical information about the surrounding area is provided in response to information of the position of a portable digital assistant, as well as in a position management system which monitors positions of commercial vehicles or police vehicles.
An example of a conventional position informing apparatus is described in Japanese Patent Application No. Hei. 11-83529, and the configuration of the apparatus is shown in FIG. 13. As shown in FIG. 13, reference numeral 1 designates position-measuring means, such as a GPS receiver; 1a designates a position-measuring antenna for receiving a signal from a GPS satellite; 27 designates a control section for controlling activation/deactivation of power to the position-measuring means 1; 11 designates communications means, such as a portable cellular phone or a PHS; 11a designates a communications antenna; 9 designates a storage section for storing the result of position-measuring; 28 designates an acceleration sensor; and 29 designates a gyroscope serving as a directional sensor.
By reference to FIG. 13, the operation of the conventional position informing apparatus will now be described. The acceleration sensor 28, the gyroscope 29, and the control section 27 operate at all times. Power is supplied also to the storage section 9 at all times, thus enabling retention of stored data. The control section 27 determines a travel distance from the acceleration information obtained by the acceleration sensor 28 and the directional information obtained by the gyroscope 29. When the travel distance exceeds a given value, the control section 27 turns on power to the position-measuring means 1. On the basis of the signal received by the position-measuring antenna 1a, the position-measuring means 1 tracks three satellites or four or more satellites and completes computation of the position of the position informing apparatus. Then, the thus-computed current position is stored in the storage section 9, and power to the position-measuring means 1 is turned off.
The communications means 11 is usually held in a standby state. When access is made to the communications means 11 from the outside, a request for current position is sent to the control section 27. The control section 27 reads the current position from the storage section 9 and sends the thus-read position to the communications means 11. The communications means 11 sends the current position to the outside by way of the communications antenna 11a. 
Thus, even the conventional position informing apparatus can provide information of a current position without power to the position-measuring means 1 remaining ON at all times.
In the conventional position informing apparatus, the gyroscope 29 and the acceleration sensor 28 remain operative at all times, thus involving dissipation of a large amount of current.
The present invention is aimed at solving the problems of the conventional position informing apparatus described above and reducing the amount of current to be dissipated by the position informing apparatus.
In order to solve the foregoing problems, the present invention provides a position informing apparatus comprising: position-measuring means for measuring the current position of the position informing apparatus; a control section for controlling power to the position-measuring means; communications means having a position-measuring request button; and means for turning on power to the position-measuring means only when a position-measuring request button is pressed, thereby effecting position-measuring operation.
By means of such a configuration, the position-measuring request button is pressed only when current position information is required, thereby turning on power to the position-measuring means and performing position-measurement. As a result, circuits or components which would be operative at all times are eliminated, thereby reducing dissipation of an electric current.
Further, the position informing apparatus is equipped with a storage section for storing a position and a timer for periodically outputting an instruction for effecting position-measurement. By means of such a configuration, the position of the position informing apparatus is periodically stored. Even at a position where position-measurement cannot be effected even when a position-measuring request is made; for example, a tunnel, position information becomes available even when only somewhat outdated position information is available.
The position informing apparatus is further comprising means for supplying power individually to a signal demodulation section and a position-measuring computation section of the position-measuring means; means for turning on power to only the signal demodulation section until position-measurement information is received; and means for turning off power to the signal demodulation section by means of turning on power to the position-measuring computation section upon receipt of position-measurement information. Such a configuration enables a reduction in mean electric power consumed by the position informing apparatus.
The position informing apparatus is further provided with means for supplying a clock individually to a signal demodulation section and a position-measuring computation section of the position-measuring means; means for supplying a clock signal to only the signal demodulation section until position-measurement information is received; and means for stopping supply of the clock signal to the signal demodulation section by means of supplying a clock signal to the position-measuring computation section when position-measurement information is received. Such a configuration enables a reduction in mean electric power consumed by the position informing apparatus, by means of supplying a clock signal to only a required portion.